Thermodynamic modelling of high salinary phosphate solutions. I. Binary systems

• Thermodynamic modelling of phosphate solutions of high ionic strengths.
• Comprehensive revision and addition of thermodynamic data by the isopiestic method.
• Interaction Pitzer parameters of phosphate ions in the hexary oceanic system.
• Reliable thermodynamic properties of phosphates solid phases.
• Physicochemical interpretation of Pitzer parameters.

A comprehensive set of interaction parameters for the thermodynamic modelling of PO43−, HPO42− and H2PO4− in concentrated solutions in the Na–K–Cl–SO4–H2O system at 25 °C was calculated by regression of experimental isopiestic and solubility data with the Pitzer formalism. The isopiestic method was used to generate additional sets of activity data, which complete and improve the statistical quality of data extracted from an extensive literature review. Thermodynamic properties of phosphate phases were calculated. In this first part, binary systems are presented.